Expandable Li Percolation Network: The Effects of Site Distortion in Cation-Disordered Rock-Salt Cathode Material

Abstract

Cation-disordered rock-salt (DRX) materials receive intensive attention as a new class of cathode candidates for high-capacity lithium-ion batteries (LIBs). Unlike traditional layered cathode materials, DRX materials have a three-dimensional (3D) percolation network for Li+ transportation. The disordered structure poses a grand challenge to a thorough understanding of the percolation network due to its multiscale complexity. In this work, we introduce the large supercell modeling for DRX material Li1.16Ti0.37Ni0.37Nb0.10O2 (LTNNO) via the reverse Monte Carlo (RMC) method combined with neutron total scattering. Through a quantitative statistical analysis of the material’s local atomic environment, we experimentally verified the existence of short-range ordering (SRO) and uncovered an element-dependent behavior of transition metal (TM) site distortion. A displacement from the original octahedral site for Ti4+ cations is pervasive throughout the DRX lattice. Density functional theory (DFT) calculations revealed that site distortions quantified by the centroid offsets could alter the migration barrier for Li+ diffusion through the tetrahedral channels, which can expand the previously proposed theoretical percolating network of Li. The estimated accessible Li content is highly consistent with the observed charging capacity. The newly developed characterization method here uncovers the expandable nature of the Li percolation network in DRX materials, which may provide valuable guidelines for the design of superior DRX materials.

Lithium-rich sulfide Li2Ti1−xSixS3 cathode materials optimized through Si-doping for high-capacity all-solid-state lithium-ion batteries

“…It has been reported that the activation of tetrahedral vacancies and the distribution of the overall percolation network are related to the cation disorder and short-range ordering arrangement in the material. 18,24 As illustrated in Fig. 3d, the smaller radius of Si 4+ possesses a stronger polarization ability than Ti 4+ and Li + .…”

“…8–12 Several transition metals such as Mn, Ti, V, and Cr have been utilized to synthesize DRXs with capacities of up to 300 mA h g −1 . 13–17 Transition metal cation mixing, 11,18 short-range ordered structure analysis, 19–22 and the Li + migration mechanism 23–26 are highly researched to activate the high capacity and improve the rate performance of DRXs. Recently, Konuma et al reported a “near dimensionally invariable” material Li 8/7 Ti 2/7 V 4/7 O 2 , which was encapsulated in Li 6 PS 5 Cl-based ASSBs using a PEEK mold and achieved a capacity of 300 mA h g −1 at a high operating pressure of 200 MPa and a current of 0.2 C (60 mA g −1 ).…”

Structure, Lithium-Ion Conductivity Coupled with Second-Order Jahn–Teller Effect, and Electrochemical Stability of Sr-Based Perovskite-Type Solid Electrolytes

“…In addition, the variation in the distortion of the BO 6 (B = Ti3, Ta3) that is very distant from the mobile Li ion is much smaller than the variations in the distortion of the BO 6 (B = Ti1, Ti2, Ta1, Ta2), indicating that the change in SOJT distortion of the BO 6 was strongly correlated with Li-ion diffusion. In a recent study on cation-disordered rock-salt materials with TiO 6 as cathode candidates for high-capacity LIBs, the specific influence of TiO 6 distortion on Li percolation was elucidated in detail . The distortion of BO 6 assisting Li-ion diffusion may be a common feature in solid electrolytes and electrode active materials for LIBs that contain d 0 B ions.…”

Nickel-Doped Titanium Oxide with Layered Rock-Salt Structure for Advanced Li-Storage Materials

“…The valuable effect of Ni doping was to add the bonus of increased charge–discharge capacity to the excellent cycling stability of the layered rock-salt type. This strategy must be valuable not only for TiO 2 -based anode materials but also metal-oxide-based cathode materials with a cation-disordered rock-salt structure, , Ni-rich layered structure, and phosphate olivine structure …”